1. Field of the Invention
The present invention relates generally to an apparatus for providing a telematics service, and more particularly to a telematics system including an AGPS (Advanced Global Positioning System) function and a mobile communication terminal.
2. Description of the Related Art
Telematics is a compound of “telecommunication” and “informatics”. Telematics is a technique for providing a mobile communication service and a position tracking service to a vehicle so as to provide information about a vehicle accident, a vehicle burglary, a driving route, traffic and life information, and games in real time. Telematics systems provide services in relation to a present position of a user, so telematics systems are based on a GPS (global positioning system) capable of detecting the present position of the user.
GPS has been designed for military use by the ministry of defense. However, some GPS functions have been permitted to be used by private businesses. The GPS satellite signals, which are permitted to be used by private businesses, are created by modulating signals, which are obtained by multiplying navigation data by a pseudo random noise code of each satellite, into a carrier. Navigation data is transmitted from the GPS satellite with a transmission speed of 50 bps and enables the user to recognize a position of the GPS satellite. The navigation data includes information about a normal operating state of the satellite, parameters for calculating a satellite clock error, ephemeris information of the satellite, and compensating values for determining a time delay of signals caused by an ionospheric layer.
A GPS receiver receives GPS satellite signals in order to demodulate the carrier and the pseudo random code, and to decode navigation data contained in the GPS satellite signals.
A mobile communication terminal equipped with the GPS receiver determines its position by measuring a distance between a satellite and the mobile communication terminal, after precisely calculating a position of the corresponding satellite based on the navigation data. The distance between the satellite and the mobile communication terminal, which is called a “pseudo-range”, may be obtained by calculating a wave arrive time from the satellite to the mobile communication terminal, after measuring a phase of the pseudo random network code of each satellite included in the GPS signals.
In addition, different from a receipt manner for a general CDMA signal, signal searching and tracking processes must be simultaneously performed in carrier and code areas when receiving the GPS signal because the GPS signal is subject to a Doppler shift (few kHz) due to rapid movement of the satellite. Consequently, it takes a long time to measure an initial position by using the telematics system measuring the position based on the GPS signal. In addition, an alignment of the satellites is designed such that at least six GPS satellites may be observed from anywhere on the earth. However, a multi-path or an attenuation of the signal may occur due to obstacles, such as buildings or street trees. As a result, it is commonly for only three satellites or less are observed.
FIG. 1 is a block view illustrating a conventional telematics system. Referring to FIG. 1, the conventional telematics system comprises a telematics terminal 10 including a GPS receiver 11, a processing section 13, and a communication section 15, a telematics server 20, and a mobile communication system 30.
FIG. 2 is a schematic view illustrating a service procedure by using present position information of the conventional telematics system. Hereinafter, the service procedure using present position information of the conventional telematics system will be described with reference to FIGS. 1 and 2.
Initially, the telematics terminal 10 receives the GPS signal and measures a present position. The telematics terminal 10 then transmits the measuring result to the telematics server 20 in order to request a service in relation to present position information in step S11. Accordingly, the GPS receiver 11 receives the GPS signal from the GPS satellite and transmits the GPS signal into the processing section 13. The processing section 13 measures the present position of the telematics terminal 10 and transmits present position information to the communication section 15. The communication section 15 transmits present position information in the form of a message to the telematics server 20. In addition, in a route guide service, the communication section 15 transmits destination information requested by the user to the telematics server 20 by adding destination information to the present position information in the form of a message.
Therefore, the telematics server 20 creates various types of service information in relation to the present position of the telematics terminal 10 by using present position information transmitted from the telematics terminal 10 in step S13 and provides services in relation to the present position of the telematics terminal 10 to the telematics terminal 10 in step S15.
As described above, the conventional telematics system must sequentially search a search area, which consists of frequencies and codes with respect to each satellite, in order to enable the telematics terminal 10 to obtain the GPS signal, if information is not provided. In addition, the conventional telematics system does not use satellite ephemeris information and user position/time information.
Therefore, the conventional telematics system takes a long time to measure an initial position of the telematics terminal, and a start time for the service may be delayed.